1. Field of the Invention
This invention relates to a carburetor for use in an internal combustion engine. More particularly, it relates to a carburetor equipped with the so-called auto-choke device wherein the degree of opening of a choke valve is automatically controlled by a thermosensitive member during the idling of the engine.
2. Description of the Prior Art
In an auto-choke device of a carburetor as has been generally known, in order to improve the starting of an engine, that is, in order to enhance the ignitability of a mixture within a combustion chamber, a choke valve of the carburetor is closed by a thermosensitive member so as to supply a thick mixture to the engine.
When the engine has started rotating by itself, the aforecited mixture is too thick. Therefore, a suction negative pressure generated downstream of a throttle valve of the carburetor is applied to a diaphragm device mechanically interlocked with the choke valve, whereby the choke valve is forcibly opened to a predetermined degree of opening called the degree of complete explosion opening, so as to form a mixture at a density suitable for continuing the subsequent rotation of the engine. This mechanism is known as what is called the complete explosion-correction mechanism.
This type of auto-choke device of the carburetor is used in a state of very low temperatures of and below -7.degree. C. and in a state of ordinary low temperatures such as +15.degree. C. Nevertheless, the complete explosion opening is fixed for the very low temperature state and the ordinary low temperature state in the complete explosion-correction mechanism as described above, and there have been the following problems:
(1) When the complete explosion opening has been set in conformity with the very low temperature state, the mixture to be supplied during the continuous running becomes unnecessarily thick in the ordinary low temperature state, and noxious components in an exhaust gas increase conspicuously. Further, it is sometimes the case that the mixture thickens beyond the inflammability limit, that the continuous running becomes difficult and that the engine stops. (2) Conversely, when the complete explosion opening has been set in conformity with the ordinary low temperature state, the mixture is too thin in the very low temperature state, and the continuous running is hindered.
In order to eliminate these drawbacks, there have been proposed an apparatus wherein two diaphragm devices are interlocked with a choke valve, the stroke of one of the diaphragm devices is made greater than that of the other diaphragm device, and the diaphragm devices are selectively used, whereby the complete explosion opening is controlled in two stages so as to get rid of the drawbacks, and an apparatus wherein as disclosed in U.S. Pat. No. 3,872,847, a diaphragm device is provided with a bimetal, whereby the complete explosion opening is controlled so as to get rid of the drawbacks.
With the former expedient, however, the selective use of the two diaphragm devices leads to the problems that the number of components becomes large and that the carburetor itself becomes large and complicated. The latter expedient has the problems that since the bimetal is exposed to the exterior, it is liable to be handled by mischief, and that an accurate degree of complete explosion opening cannot be attained by only the force of the bimetal.